This invention relates to a graphic display method and, more particularly, to a graphic display method for transforming the three-dimensional coordinate values of an object to be displayed into the coordinate values of a two-dimensional display coordinate system, and displaying a perspective view of the object on a CRT display screen by using the two-dimensional coordinate values obtained by the transformation, wherein the position at which the perspective view is displayed can be shifted, and the perspective view rotated, in a simple manner.
Graphic display units are in use everywhere as means for implementing CAD/CAM (computer aided design and manufacturing). It is essential that these graphic display units be capable of displaying the perspective view of a three-dimensional object on a display screen (CRT screen). To this end, conventional graphic display units are adapted to display a perspective view of a three-dimensional object and are capable of enlarging and reducing the size of the displayed view.
There are situations where it is desired to shift the position at which the perspective view is displayed on the CRT screen or to display the perspective view on the CRT screen upon changing the position from which the three-dimensional object is observed. In other words, there are times when one wishes to display the perspective view on the CRT screen while the view is rotated. In such cases, the conventional practice is to enter the display position and the angle of rotation from a keyboard to change the position at which the perspective view is displayed or to display the perspective view upon rotation.
With the conventional practice however, operation is troublesome, the display position cannot be changed continuously, and the perspective view cannot be displayed while it is being continuously rotated.
In addition, specialized hardware such as a joystick is provided and the joystick is used to change the display position or the angle of rotation of the perspective view. Thus, extra hardware is required, which is undesirable in view of cost.